Sealants can be poured into the several injectors from a filing hole of each injector in the same time and same speed. Actually, a coating length of each injector is different. So a sealant wastage in each injector is also different. The sealant wastage of two injectors in two opposite sides is more than that of in the middle. When the coating process is over, the sealants of two injectors in both two sides is exhausted and the sealants in the middle is remained. Then the unused sealants are wasted.